Stuttgart 2012 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 13: Photoionization
A 13.3: Vortrag
Dienstag, 13. März 2012, 11:00–11:15, V55.01
Evidence for anisotropic final state interactions in the two-photon ionization of He — •Gregor Hartmann1, Markus Braune2, Toralf Lischke1, Andre Meissner1, and Uwe Becker1 — 1Fritz-Haber-Institut der Max-Planck Gesellschaft, Faradayweg 4-6, 14195, Germany — 2DESY, Notkestr. 85, 22067 Hamburg, Germany
The photoelectron angular distribution of single photoionization is described by Legendre Polynomial of second order P2(cosθ). Two-photon ionization however, gives rise to a second term being a Legendre Polynomial of fourth orderP4(cosθ). This Term for sequential two-photon ionization has a weighting factor given by the alignment of the ionic core left by the first ionization step. If this first step leaves an isotropic core this alignment is zero and the corresponding P4 term should have no actual effect on the photoelectron angular distribution. In order to prove this theoretical prediction we have performed two-photon ionization experiments at Helium. At higher photon energies the angular distribution of the second step photoelectron followed indeed a P2-distribution as expected. However, at lower photon energies the photoelectron angular distribution showed small P4 behavior. We interpret this unexpected result as evidence for anisotropic final state interaction due to a first step final state consisting of a combined system of ionic core and outgoing photoelectron.